In the field of composite rocket propellants useful in various rocket motors, increasing the burn rate is a constant challenge. Such an increase in the burn rate of such solid propellants leads to an increase in the mass flux of combustion gases and therefore an increase in the thrust generated by the motor. One of the critical features in the ability to develop improved motors of this type has been the introduction of burning rate catalysts which accelerate the burning rate of the rocket propellant. Of the wide number of such catalysts one, iron oxide, has proven to be quite successful. It has further been discovered that for optimum efficiency and performance of these catalysts, it is desirable to have the iron oxide particles as small as possible and preferably smaller than 100 angstroms. The manufacture and the use of iron oxide catalysts and propellants utilizing such catalysts are set forth in commonly assigned U.S. Pat. No. 4,854,981 the disclosure of which is incorporated herein.
The manufacture of such iron oxide, as described in the above referenced patent and depicted in schematic form in FIG. 1 herein, comprises introducing a gas stream of iron-containing compound, which has been mixed with a non-oxidizing gas, 2 through an injector 4 into a stream of hot oxidizing gas 6 which has been heated by a heater 8 inside a reactor chamber 10. The dilute iron-containing compound then contacts the hot oxidizing gas, which is forced through the reactor 10 by a blower 12 and thereby causing the iron-containing compound to oxidize to iron oxide in very fine particle sizes 14.
The drawback to the above described method is that during extended production runs some of the oxidation of the iron-containing compound to iron oxide occurs at the tip or port 16 of the injector 4 where the iron-containing compound mixture enters the reaction chamber 10 causing a build-up of iron oxide at the port 16. This, obviously, impairs the operation of the injector and just as importantly results in the development of undesirably large iron oxide particles which slough off during production runs thereby contaminating the iron oxide product.
One method which addresses the problem resulting from the operation of the '981 patent is discussed in pending U.S. patent application Ser. No. 283,117 and which is commonly assigned and is also incorporated herein a schematic of which is set forth herein as FIG. 2. This method is very similar to the previously discussed method in which a gaseous stream of an iron-containing compound 2 is introduced into a reactor duct 10 through an injector 4 and into an oxidizing gas 6 which is heated to an appropriate temperature by heater 8 and is simultaneously forced through the reactor duct by a blower 12. However, in this invention the iron-containing compound is diluted with a stream of cool oxidizing gas which is blown through a feed duct 18 by blower 20. The output of the feed duct 18 discharges into the stream of hot oxidizing gas in reactor duct 10. This resulted in a more complete reaction between the iron compound and the oxidizing gas and prevented the growth of iron oxide particles at the injector port 16. However, it has been discovered that even this improvement was subject to the deposition of iron oxide on the wall of the reaction chamber 22 downstream from the point of entry of the cool iron-containing compound gas/oxidizing gas where the gas mixture contacts the hot reactor wall. This deposit is at a temperature well above that at which the fine iron oxide particles anneal and lose surface area. When the layer of dense, annealed material grows thick enough, it sloughs off, enters the stream of iron oxide particles and contaminates the desired low density, high surface area iron oxide product.
Therefore, what is needed in this art is an improved method for producing the iron oxide particles having high surface area, low density and very small particle sizes and which can be operated free of the problems connected with the prior methods.